Hair styling formulations are desired that provide both good hold (i.e., the ability to hold hair in place) and good shine (i.e., the ability to give hair a shiny appearance). Additionally, clarity (translucent appearance) of the hair styling formulation prior to application is aesthetically important to consumers.
Typically, hair styling formulations include one or more polymers which serve as the hair fixative. While there are many polymers that provide good hold in hair styling formulations, some of them negatively impact other properties such as shine or clarity.
Hair styling formulations also typically include an appropriate solvent. The class of volatile organic compounds (VOCs) which are liquid at 25° C. and one atmosphere pressure are generally useful as volatile organic solvents in hair spray formulations. Because hair styling formulations are sometimes sprayed, it is desirable that any polymers used in the formulation dissolve fully in the solvent. Further, for proper spraying, it is desirable that a solution of any polymers used in the composition should have viscosity that is not too high.
Where a hair styling formulation is to be applied in an aerosol spray, the solvent also includes one or more propellants, which may be volatile non-organic compounds or VOCs and are gaseous at 25° C. and one atmosphere pressure. For example, without limitation, it is known to use carbon dioxide, propane, isobutane, dimethyl ether and tetrafluoroethane, among other materials, as the aerosol propellant for such formulations.
It is also desirable that the hair styling formulation be stable (i.e., that none of the ingredients settles while the formulation is in storage). It is known that as the volatile organic compound (VOC) content of a formulation containing certain polymers increases, a haze appears, and increases, in the formulation, due to incompatibility of the polymer with solvents and propellants. This haze may negatively effect long term shelf life stability and also may be aesthetically unpleasing to consumers.
Thus, selecting the types and proportions of ingredients for hair styling formulations is very important and can be difficult. It is desired to provide polymers which have good hold characteristics, without negatively impacting the levels of shine and clarity in hair styling formulations.
One approach to improving the water compatibility of carboxylated vinyl polymeric hair spray resins in alcohol hydrocarbon propellant systems has been to neutralize at least a portion of the available carboxyl functionalities of the resins, as described in U.S. Pat. No. 4,192,861, using alkaline reagents.
U.S. Pat. No. 4,315,910 describes aerosol hair spray compositions used in aerosol metal containers that contain polymer, including, for example, styrene/maleic anhydride polymers, as well as carbon dioxide or hydrocarbon-alcohol propellants and 1-15% by weight water. It is asserted in U.S. Pat. No. 4,315,910 that addition of the water to this composition improved shelf stability and compatibility of the polymer in these compositions compared to anhydrous formulations using carbon dioxide or hydrocarbon-alcohol in aerosol metal containers.
It is also known to improve the clarity of non-aerosol, gel hair styling formulations containing silicone grafted co-polymers by neutralization with organic or inorganic neutralizer or mixtures thereof. GB 2291893A describes an aqueous/alcohol hair styling gel containing a silicone-containing polycarboxylic acid polymer and selected organic neutralizing agents that is claimed to have further improved clarity as well as non-sticky in-use feel and easy brush-out characteristics.
It has been discovered that some polymers, produced by emulsion polymerization and used in hair styling formulations, contain oligomer side products which increasingly precipitate and settle out of the formulation solution as the VOC content of the formulation increases. Thus, an object of the present invention was to identify and synthesize polymers having less oligomer side product or having oligomers which are more compatible with the VOCs used in hair styling formulations.